The present invention relates to an electrically-operated injection molding machine using a servo motor as a drive source of the injection molding process, and more specifically to an electrically-operated injection molding machine for super-precision molding using servo motors for a product eject process and a molding removal process as well as an injection compression molding method using the relevant machine.
The injection molding machine using servo motors for drive sources of each process has been popularly used now. However, even in such event, servo motors are used at most for drive sources, such as (1) injection into die cavities of weighed resin, (2) weighing of blended resin, (3) opening and closing of dies, (4) gate cutting, etc., and there has been no case in which servo motors are used in the product eject process. This is because as shown in FIG. 21, the location of screw mechanism for gate cutting is concentrated with an extremely large number of mechanisms, and an air cylinder has conventionally been used for drive sources of the product eject pin for a device that can be barely contained in this portion.
First Problem
As observed recently, when the high cycle of injection molding machines advances gradually, the time for removing ejected products causes problems. An attempt to shorten time naturally requires accurate response at this portion. However, the air cylinder has limitations in response speed as well as variations in response timing, and the shortening and improvement in accuracy in product removal from the air cylinder have reached their limits.
To show one example, assume that the desired production cycle time per product is 3 seconds, the time assigned from eject to product removal is 0.12-0.15 second, whereas when an air cylinder is used, 0.2 second is required, and approaches by the air cylinder become extremely difficult.
In addition, because there are variations in repetitive response accuracy of the air cylinder on order of 0.01 second, an allowance from 0.02-0.05 second must be provided for timing of product removal carried out by a product removing equipment (not illustrated), and when still higher cycle is aimed at, the air cylinder has a problem of large time loss in shortening of the overall time.
Second Problem
In the electrically-operated injection molding machine of the conventional example using servo motors, each servo motor is feedback controlled in each process based on the program data for servo control. This takes in the data from the encoder equipped to the relevant servo motor into CPU for arithmetic, and the position, speed, torque, etc. are feedback controlled as specified in the program.
However, this kind of control method is an indirect control method of the position, speed, torque, etc. via the encoder equipped to the servo motor, and has been unable to directly detect injection pressure, weighed resin pressure, and die clamping force, etc. actually applied to the screw and dies and to feedback control based on the actually detected data. That is, because it was unable to find any place to install a pressure sensor for directly detecting the die clamping force applied to the dies, it was unable to directly detect the die clamping force and carry out feedback control.
Third Problem
In the electrically-operated injection molding machine which uses many servo motors, using one servo motor for one operating mechanism results in too many servo motors, causing disadvantages of not only enormous equipment costs but also complicated control.
Fourth Problem
Recently, the digital technique has been popularized in various fields including data processing, images, and music, and as a natural consequence, for example, CD, MD, DVD, and other digital substrates have been put into practical use. In particular, in PVD substrates, it is required to transfer super fine protrusions and recessions formed on dies accurately to moldings, and hydraulically-controlled conventional injection molding machines are no longer able to satisfy the requirements.
Consequently, injection molding machines which use many servo motors as described above, though partly, have been developed. And as this kind of increased precision of injection moldings advances, not only injection molding machines but also injection molding methods have continuously evolved. In this kind of injection molding machines, the following will govern the substrate accuracy.
For example, taking molding of optical disk substrates for example, warpage of moldings, adhesion of foreign matter, void, discoloration by gas, molding cycle, etc. constitute extremely important factors, but above all, the biggest problems are (1) super fine pitch, (2) pit transferability of depth, (3) realization of double refraction of 50 nm or less, and it is possible to suppress double refraction by alleviating (photoelasticity coefficient x main stress difference [=shear stress+thermal stress]).
Now in substrate molding, (1) microvoids and (2) micro flowmarks can be mentioned for factors that check transferability of fine protrusions and recesses.
That is, when resin flows along fine protrusions and recessions, air entrapping phenomena occurs in the resin flow in the front and the rear of the wall of fine protrusions and recessions, and fine air pools are formed. This fine air pool causes degraded transferability, and the countermeasure is to suppress resin solidification by high-speed filling as much as possible and to complete filling. However, this was insufficient. by conventional injection molding method. In addition, timing of injection compression is an important factor.
The foregoing description can be summarized as follows. In these several years, practical application and its development of digital substrates have been remarkable, and new deployment of injection molding machines and injection molding technique has been called for. At the same time, the demand for still higher cycle of forming speed has been exceptional, and for a solution, adoption of the servomechanism of all the drive units has been promoted.
(1) It is the screw mechanism for ejection for removing moldings from dies and direct detection of resin filling pressure and clamping force to dies at the die portion that constitute bottlenecks in adopting servomechanism. Even if pressure sensors are intended to be installed to the movable die side for directly detecting resin filling pressure or die clamping force, there is a limitation in space, and even when the pressure sensor is installed on the movable die side, there is a restriction in that the screw mechanism for ejection is unable to be installed unless some special construction is adopted, and in addition, it is also a limit in space.
(2) The adoption of servomechanism naturally means feedback control, but because in conventional cases, actual resin filling pressure and die clamping force were unable to be detected, they must be processed by feedback control using the data from the encoder attached to the servo motor.
(3) The reduced number of servo motors is quoted as one of the requirements together with adoption of servomechanism.
(4) Another object of requirements for adoption of servomechanism lies in improvement of transferability of super fine protrusions and recessions for, for example, optical digital substrates.
Now, problems the present invention intends to solve are described as follows in due order.
To consider in this way, if further higher cycle is intended, epochmaking innovation in the product eject system has been desired with respect to the first problem to be solved, because the product ejection by an air cylinder has already reached its limit. In other words, the object of this invention is (1) to develop a novel mechanism that can substitute for the cylinder system in order to achieve still higher cycle and to enable product removal without time loss in linkage with this new mechanism, and (2) to be able to install the new mechanism that substitutes for the cylinder system smoothly to a complicated gate cut mechanism portion.
In the second problem to be solved, because the servo motor is used for a driving source, it is an object of this invention not only to achieve higher cycle but also to directly detect weighed resin pressure and die clamping force exerted to dies in order to carry out feedback control. In particular, it is an object of this invention to enable direct detection of die clamping force on the die mechanism side, which has been considered impossible.
The third problem to be solved is to allow one servo motor to carry out two or more tasks to reduce the number of servo motors, because the use of many servo motors results in increased costs and complication of control, and it is an object of this invention to achieve reduction in manufacturing costs and simplification in control without degrading the performance by allowing one servo motor to cover gate cutting and molding ejection processes.
The fourth problem to be solved is to develop an injection molding method in an electrically-operated injection molding machine using servo motors for simultaneously achieving requirements for higher cycle of forming, improved transferability of fine protrusions and recessions formed on the dies, and stabilization of the molding quality, and control of speed for injecting weighed resin to die cavity, control of gate cutting timing, die compression speed, and die compression pressure as well as positional control of dies for achieving uniform molding thickness must be properly carried out to achieve this, and these requirements have never been achieved with the capabilities of conventional equipment which has employed a hydraulically-driven die compression forming method.
The fifth problem to be solved is to further improve the transferability of fine protrusions and recessions by eliminating fine air pools generated between fine protrusions and recessions and the solidified skin layer through eliminating the generation of the solidified skin layer as much as possible with further improvement in the die compression forming method.
The first configuration of the invention is to achieve the first object and is characterized by an injection molding machine (A) used for a precision forming injection molding method that has servo motors ( 1), (12), (31), (40), (45), and (51) used for driving sources in processes of weighing blended resin (3b), of injecting weighed resin (3a) into a die cavity (2), of opening and closing dies, of gate cutting after filling weighed resin (3a) into the die cavity (2), of ejecting the molding (26) after forming, and of removing the molding (26).
According to this configuration, because all the motions of injection operation are controlled by servo motors (11), (12), (31), (40), (45), and (51), the timing, injection speed, pressurizing speed, pressurizing pressure, and all others can be freely controlled, and not only the transferability of fine protrusions and recessions formed on the inner surface (5) of the die cavity (2) can be remarkably improved, but also the cycles can be increased because complex motions can be carried out by servo motors (11), (12), (31), (40), (45), and (51).
In particular, because servo motors (45), (51) are used for driving sources of ejection of molding. (26) after forming and removal of molding (26), there is no variation in repetitive response accuracy in motion, product removal timing by the product removing equipment (S) can be reduced to 0.01 second or less, and ultimately higher cycle is able to be achieved.
The second configuration of the invention is characterized by an injection molding machine (A) having:
(a) a gate cutting screw mechanism (G);
(b) a gate cutting member (30) connected to said gate cutting screw mechanism (G) and placed to a movable die (1b) where it is allowed to make reciprocating movements freely;
(c) a servo motor (51) for operating said gate cutting member (30) via the gate cutting screw mechanism (G);
(d) an ejection screw mechanism (E);
(e) an ejection member (27) connected to said ejection screw mechanism (E) and placed to the movable die (1b) where it is allowed to make reciprocating movements freely;
(f) a servo motor for operating the ejection member (27) via the ejection screw mechanism (E),
wherein a screw shaft (30a) of the gate cutting screw mechanism (G) and a center ejecting bar (27a) of the ejection screw mechanism (E) are arranged on the same axis, and the center ejecting bar (27a) is inserted in the screw shaft (30a);
and the gate cutting screw mechanism (G) is located closer to the dies(1) than the ejection screw mechanism (E).
According to this configuration, because the gate cutting screw mechanism (G) and the ejecting screw mechanism (E) are aligned in one line and the straight portion (27b) is inserted in the screw shaft (30a), the gate cutting screw mechanism (G) and the ejection screw mechanism (E) with complicated mechanisms can be smoothly located in this portion.
The third configuration of the invention relates to the removal of a molding (26) in order to achieve the first object, wherein the injection molding machine (A) includes:
(a) a product removing equipment (S) controlled by a servo motor (45);
(b) an ejection screw mechanism (E) controlled by said servo motor(51);
(c) the product removing equipment (S) for removing the molding (26) from said movable die (1b) under a condition with little time loss or free of time loss by electrically controlling a timing for ejecting said molding (26) from the die cavity (2) and the timing for removing the molding (26) by operating the ejection screw mechanism (E). As described before, the repetitive response accuracy is free of variations when the molding (26) is ejected and the molding (26) is removed after molding. The product removal timing by the product removing equipment (S) can be 0.01 second or less, enabling the achievement of ultimate higher cycle.
The fourth configuration includes a means for solving the second problem, and relates to feedback control of the die clamping force by a pressure sensor (7) on the movable die (1b) side of the injection molding machine (A) having:
(a) a movable die plate for mounting said movable die (1b);
(b) a housing (50) with a toggle mechanism (T);
(c) a pressure sensor (7) placed between said movable die plate (18) and said housing (50):
(d) a servo motor for driving a toggle mechanism (T);
(e) and servo motors (11),(12) for injection control,
wherein in a resin filling process,
a reactive force of said movable die (1b) due to filling resin (3) in the die cavity (2) is detected by said pressure sensor (7);
resin injection into the die cavity (2) is feedback-controlled based on an output data of said resin (3) filled from said pressure sensor (7);
and in a die compression process and a following pressure-holding process,
the feedback control on the die clamping force by said servo motor (31) and position control of said movable die (1b) are carried out based on the data from said pressure sensor (7).
According to this, because the pressure sensor (7) is placed between the movable die plate (18) and the housing (50), direct detection of resin pressure, die clamping force, or position control of the movable die (1b) at the time of injection filling which has been difficult to date has been made possible, and more accurate feedback-control of die clamping force and die-clamping stopping position has been enabled.
The control is applied in all the processes such as (1) part of the injection process from when filled resin (3) begin to come in contact with the dies (1) to gate cutting, (2) timing of gate cutting for closing the gate (1c) of the filled resin (3), process for compressing the filled resin (3) with dies (1), pre-stage of the pressure-holding process, and (4) position control, post-stage of the pressure-holding process.
The fifth configuration is an example of the pressure sensor (7) being between the movable die plate (18) and the housing (50) wherein a molding eject mechanism (E) is provided. An ejection member (27) for ejecting molding (26) is inserted in the movable die (1b) through the pressure sensor (7).
Another configuration includes an injection molding machine having:
(a) an ejection screw mechanism (E) equipped to the housing (50);
(b) ejection members (27) which are parts of said ejection screw mechanism (E) for ejecting the molding (26) in the die cavity (2) are inserted in the movable die (1b) through the pressure sensor (7). Consequently, if the pressure sensor (7) is intended to be installed, the molding ejecting mechanism (E) must be designed specially in such a manner to avoid the pressure sensor (7) as shown in FIGS. 1-6, and before this invention, there is no case in which the pressure sensor (7) is located between the movable die plate (18) and the housing (50).
However, this problem can be solved by providing a penetration hole (7a) in the pressure sensor (7), and the injection pressure, weighed resin pressure, and die clamping force exerted to dies (1) have been able to be directly detected by the pressure sensor (7).
A further implementation relates to a means for solving the third problem relative to an injection molding machine having:
(a) a hollow gate cutting member (30) slidably placed in the movable die (1b);
(b) an ejection member (27) slidably inserted in the gate cutting member (30);
(c) a gate cutting drive nut portion (44) for forwarding and reversing the gate cutting member (30), screwed to the threaded portion (30a) formed on the outer side of the screw shaft which is a part of the gate cutting member (30);
(d) an eject nut portion (49) for forwarding and reversing the ejection member (27), screwed to a screwed portion (27s) of the center eject bar which is the part of said ejection member (27);
(e) a pulley for simultaneously rotating the gate cutting drive nut portion (44) and the eject nut portion (49);
(f) and the gate cutting drive nut portion (44) and the eject nut portion (49) are inversely threaded each other.
According to this, because rotating the driven pulley (43) to protrude the gate cutting member (30) reverses the ejection member (27) and conversely discharging the ejection member (27) to eject the molding (26) reverses the gate cutting member (30), gate cutting and ejection of the molding (26) can be driven with one servo motor (40) and the number of servo motors can be reduced without degrading the equipment performance, and the control can be simplified.
Another aspect of the present invention relates to a first method of die compression for solving the fourth problem that is characterized by operating a die compression injection molding machine that has:
(a) a movable die (1b) mounted on a movable die plate (18);
(b) a pressure sensor for detecting reaction force of said movable die (1b) caused by resin (3) filled in a die cavity (2), placed between said movable dieplate (18) and the housing (50) connected to the toggle mechanism (T),
wherein at least, either of pressure control of filling resin (3) by the movable die (1b) or thickness control of filled resin (3) by position control of the movable die (1b) is carried out based on the output data from said pressure sensor (7).
According to this configuration, the control which is an important factor in the pressure-holding process is carried out by the reaction force directly obtained from the filled resin (3), enabling realtime and accurate control.
Another aspect of the invention relates to the control of operation timing of a gate cutting member (30) and is characterized by the die compression injection molding method operating an injection molding machine (A) for precision molding having:
(a) a movable die (1b) mounted on a movable die plate (18);
(b) a pressure sensor (7) for detecting the reaction force of said movable die (1b) by resin (3) filled in the die cavity (2), placed between the movable die plate (18) and the housing (50) connected to the toggle mechanism (T);
(c) and a gate cutting member (30) for closing the die gate (1c),
wherein an operating timing of said gate cutting member (30) is controlled based on the output data from said pressure sensor (7).
According to this configuration, timing control of gate cutting, one of the important factors in the injection molding process is carried out by the reaction force directly obtained from filled resin (3), and real-time and accurate control is achieved.
Another aspect of the invention relates to resin injection speed control by a pressure sensor (7) output and is characterized by a die compression injection molding method for a injection molding machine (A) for precision molding having:
(a) a movable die (1b) mounted on a movable die plate (18) and a stationary die (1a) mounted on a stationary die plate (17);
(b) a pressure sensor for detecting the reaction force of the dies (1) by resin (3) filled in the die cavity (2), placed between the movable die plate (18) and the housing (50) connected to the toggle mechanism (T);
(c) and the. injection mechanism portion (a) for injecting resin (3) into said dies (1),
wherein the resin injection speed control from the injection mechanism portion (a) into the dies (1) is controlled based on the output data from said pressure sensor (7).
According to this configuration, the injection process, one of the important factors in the injection molding process, in particular, injection speed control is carried out by the reaction force directly obtained by the filled resin (3), and real-time and accurate control is enabled.
Another aspect of the invention relates to a method of die compression injection molding using an injection molding machine (A) for a precision molding that includes;
(a) injecting weighed resin (3a) into a die cavity (2) of dies (1) in the course of moving- in a die closing direction of a movable die (1b);
(b) carrying out gate cutting when a specified amount of resin (3) is filled, continuously moving the movable die (1b) in the die closing direction to a specified position as it is without stopping,
(c) keeping the dies (I) clamping with holding pressure at said specified die clamping position during holding pressure process and cooling process,
(d) after said cooling process , removing the molding from the open dies (1).
According to this configuration, because the movable die (1b) is continuously moved in the die closing direction from the start of injection filling of the weighed resin (3a) to the start of die clamping, the filled resin (3) cooperates with the movement of the movable die (1b) to increase the relative speed of the filled resin (3) with respect to the movable die (1b), and as a result, the filled resin (3) comes in contact with the inner side of the die cavity (2) and flows more quickly, allowing the new resin inside to expose to the surface of the resin (3), and formation of the skin layer of the resin surface is hindered. As a result, the transferability of fine protrusions and recessions to the molding (26) is remarkably improved.
Another aspect of the invention relates to the amount of filled resin (3) in the die cavity (2) exceeding a volume of the molding (26).
According to this, because the filled resin (3) of a volume exceeding the volume of the molding (26) is compressed to the volume of the molding (26) by compression molding, the molding (26) forms a high-density substrate free of variations in density and contributes to the improvement in the quality.
Another aspect of the invention relates to forming fine protrusions and recesses for transferring to the filled resin (3) on the inner side (5) of the die cavity (2) of the movable die (1b) described above, the filled resin (3) cooperates with the movement of the moveable die (1b), increases the relative speed with respect to the movable die (1b), comes in contact with the inner surfaces (5) of the die cavity (2) in the movable die (1b) while constantly exposing the new resin inside to the resin surface, and flows quickly. As a result, the formation of the skin layer on the resin surface is hindered, and this hinders generation of fine air pools that impair the transferability.
If fine protrusions and recessions are formed on the inner surface (5) of the die cavity (2) in the movable die (1b), the transferability can be remarkably improved by this method.